When parsing permissively, don't print to stderr

[seldridge]

This removes bool permissive from htif.cc, which was originally used to control whether or not htif was parsing arguments permissively. This instead uses getopt's builtin int opterr to hold this state. getopt then uses this to print/not print to stderr on unknown options.

Resultingly, unknown VCS options will not produce any stderr output.

From discussion in https://github.com/freechipsproject/rocket-chip/pull/1266#issuecomment-370890731.

[seldridge]

@ccelio: This should do what you want.

Some options that elucidate the change are below. Now, when a short option known to VCS, but unknown to htif shows up (e.g., -q) this only results in stderr output when not parsing permissively.

• No unknown short options inside +permissive/+permissive-off

  > ./simv-freechips.rocketchip.system-DefaultConfig +permissive +ntb_random_seed_automatic +permissive-off +permissive +max-cycles=100000000 +permissive-off $RISCV/riscv64-unknown-elf/share/riscv-tests/isa/rv64si-p-wfi 3>&1 1>&2 2>&3 
  Chronologic VCS simulator copyright 1991-2013
  Contains Synopsys proprietary information.
  Compiler version H-2013.06-SP1_Full64; Runtime version H-2013.06-SP1_Full64;  Mar  6 14:30 2018
  NOTE: automatic random seed used: 1127523411
  $finish called from file "/home/schuyler/repos/github.com/freechipsproject/rocket-chip/vsrc/TestDriver.v", line 130.
  $finish at simulation time              3802050
         V C S   S i m u l a t i o n   R e p o r t 
  Time: 38020500 ps
  CPU Time:     15.000 seconds;       Data structure size: 513.8Mb
  Tue Mar  6 14:30:28 2018
  bash: __git_ps1: command not found
  schuyler@silserv1:~/repos/github.com/freechipsproject/rocket-chip/vsim$

• One unknown short option (-q) inside +permissive/+permissive-off. There is no stderr getopt complaint from inside htif.cc.

  > ./simv-freechips.rocketchip.system-DefaultConfig +permissive -q +ntb_random_seed_automatic +permissive-off +permissive +max-cycles=100000000 +permissive-off $RISCV/riscv64-unknown-elf/share/riscv-tests/isa/rv64si-p-wfi 3>&1 1>&2 2>&3 
  NOTE: automatic random seed used: 3613937659
  $finish called from file "/home/schuyler/repos/github.com/freechipsproject/rocket-chip/vsrc/TestDriver.v", line 130.
  $finish at simulation time              3778050
  bash: __git_ps1: command not found
  schuyler@silserv1:~/repos/github.com/freechipsproject/rocket-chip/vsim$

• One unknown short option (-q) outside of +permissve guards. This generates getopt stderr and an exception

  > ./simv-freechips.rocketchip.system-DefaultConfig -q +permissive +ntb_random_seed_automatic +permissive-off +permissive +max-cycles=100000000 +permissive-off $RISCV/riscv64-unknown-elf/share/riscv-tests/isa/rv64si-p-wfi 3>&1 1>&2 2>&3 
  NOTE: automatic random seed used: 3743293718
  ./simv-freechips.rocketchip.system-DefaultConfig: invalid option -- 'q'
  terminate called after throwing an instance of 'std::invalid_argument'
  what():  Unknown argument (did you mean to enable +permissive parsing?)
  bash: __git_ps1: command not found
  schuyler@silserv1:~/repos/github.com/freechipsproject/rocket-chip/vsim$

• Attempt to nest +permissive throws an exception

  > ./simv-freechips.rocketchip.system-DefaultConfig +permissive +permissive +ntb_random_seed_automatic +permissive-off +permissive +max-cycles=100000000 +permissive-off $RISCV/riscv64-unknown-elf/share/riscv-tests/isa/rv64si-p-wfi 3>&1 1>&2 2>&3 
  Chronologic VCS simulator copyright 1991-2013
  Contains Synopsys proprietary information.
  Compiler version H-2013.06-SP1_Full64; Runtime version H-2013.06-SP1_Full64;  Mar  6 14:31 2018
  NOTE: automatic random seed used: 541785289
  terminate called after throwing an instance of 'std::invalid_argument'
  what():  Found +permissive when already parsing permissively
  bash: __git_ps1: command not found
  schuyler@silserv1:~/repos/github.com/freechipsproject/rocket-chip/vsim$

• Attempt to use +permissive-off when not permissively parsing throws an exception

  > ./simv-freechips.rocketchip.system-DefaultConfig +permissive +ntb_random_seed_automatic +permissive-off +permissive-off +permissive +max-cycles=100000000 +permissive-off $RISCV/riscv64-unknown-elf/share/riscv-tests/isa/rv64si-p-wfi 3>&1 1>&2 2>&3 
  Chronologic VCS simulator copyright 1991-2013
  Contains Synopsys proprietary information.
  Compiler version H-2013.06-SP1_Full64; Runtime version H-2013.06-SP1_Full64;  Mar  6 14:31 2018
  NOTE: automatic random seed used: 3254520216
  terminate called after throwing an instance of 'std::invalid_argument'
  what():  Found +permissive-off when not parsing permissively
  bash: __git_ps1: command not found